Urine Reabsorption Flashcards
What is the “formula” for what makes up urine?
Glomerular filtration - tubular reabsorption + tubular secretion
What measurement is more vital for determining excretion rate?
Tubular reabsorption
Secretion of urine plays a role in the excretion of what ions in the urine?
Potassium and hydrogen ions
What is the general calculation of filtration for substances freely filtered and not bound to plasma proteins?
Glomerular filtration rate (GFR) X plasma concentration
How would we find the filtration of glucose per day, for example?
180 L/day (glomerular filtration) X 1 g/L (plasma concentration) = 180 g/day of glucose
Which is highly selective: tubular reabsorption or glomerular filtration?
Tubular reabsorption
Which is nonselective (except protein and substances bound to them): tubular reabsorption or glomerular filtration?
Glomerular filtration
Do the kidneys excrete all substances at the same rate?
No, everything individually based on the body’s needs
What are the four steps of the tubular reabsorption of a substance?
1 transportation across tubular epithelial membrane
2 goes through interstitial fluid
3 goes through peritubular capillary membrane
4 goes into the blood
What is the transcellular route in which water and solutes can travel through the tubular epithelium?
Through the cell membranes
What is the paracellular route in which water and solutes travel through the tubular epithelium?
Between the cells through tight junctions
How do water and solutes travel through the tubular epithelium via bulk flow/ultrafiltration which is mediated by hydrostatic pressure and osmotic flow?
Through peritubular capillary walls into the blood
How else can water and solutes travel through the tubular epithelium besides the transcellular and paracellular routes and through the peritubular capillary walls?
Through medullary interstitium fluid
Which form of active transport is coupled which hydrolysis of ATP?
Primary active transport
The sodium-potassium ATPase pump is an example of what kind of transport?
Primary active transport
What kind of active transport is coupled indirectly to the energy source like an ion gradient?
Secondary active transport
Reabsorption of glucose by the renal tubule is an example of what kind of transport?
Secondary active transport
Is water always absorbed by an active or passive mechanism? What is that mechanism?
Passive; osmosis
What is osmosis?
Diffusion of water from an area of low solute concentration to an area of high solute concentration
Where does the sodium transport system occur?
Proximal tubular membrane
Where is the sodium-potassium ATPase system located on the cell?
Cell membrane on the basolateral surface
What causes the -70 millivolt negative charge in the cell?
Active transport of sodium and potassium from inside the cell to the interstitium
Is the movement of sodium to the peritubular capillary from the intercellular fluid an active or passive process?
Passive (driven by osmotic gradient just like water)
What is the mechanism of transport of sodium from the lumen to tubular cell?
Diffusion
What is the mechanism of transport of sodium from the tubular cell to the interstitial fluid?
ATPase pump (active transport)
What is the mechanism of transport of sodium from the interstitial fluid to the peritubular capillary?
Diffusion
In what kind of transport are 2 or more substances transported across a membrane by a carrier molecule?
Secondary active transport
Sodium diffusing down its electrochemical gradient and that energy driving glucose (for example) down ITS electrochemical gradient would be an example of what kind of transport?
Secondary active transport
Where are the sodium glucose co-transporters located (SGLT2 and SGLT1)?
Brush border
What transporters are used to transport glucose into the cell against a concentration gradient (secondary active transport)?
SGLT2 and SGLT1
Which SGLT is located in the early part of the proximal tubule?
SGLT2
Which SGLT is located in the later part of the proximal tubule?
SGLT1
Which SGLT transports 90% of the filtered glucose for reabsorption?
SGLT2
Which SGLT transport 10% of the filtered glucose for reabsorption?
SGLT1
What kind of transport is responsible for the transport of glucose from the proximal tubule across the luminal membrane?
Secondary active transport (usually via SGLT 2)
What is responsible for the passive uptake of glucose into the peritubular capillary?
Bulk flow
What is counter transport?
Secretion of substance into the tubule by secondary active transport
What effect does sodium being actively transported into the cell have on hydrogen ions?
Drives hydrogen ions out of the cell into the tubular lumen (counter transport due to energy liberated from prior sodium transport)
What is transport maximum?
Limit to the rate at which a solute can be transported during active reabsorption or secretion
What is the overall average transport maximum for glucose?
375 mg/min (reached when all nephrons have reached their maximal capacity to reabsorb glucose)
What effect does aging have on transport maximum and why?
Decreased because nephrons die with age (presence of kidney conditions more prevalent in older individuals)
During what circumstance can some substances not demonstrate a transport maximum?
If absorbed passively
What three things does the rate of transport depend on?
Electrochemical gradient
Permeability of membrane to substance
Time the fluid containing the substance remains in tubule
What is the term for the type of transport where substances are passively absorbed and depend on other circumstances like electrochemical gradient, time substance-filled fluid remains in tubule, and membrane permeability?
Gradient-time transport
What effect does aging have on gradient-time transport?
Increased
Can actively transported substances exhibit characteristics of gradient-time transport?
Yes; example would be sodium reabsorption int he proximal tubule where sodium doesn’t have a transport maximum
What is the pathway for urine flow structure by structure?
Nephron –> collecting ducts –> renal calyces –> ureters –> bladder
What activity forces urine from the kidneys to the bladder and where does it occur?
Peristaltic contractions; renal pelvis and ureters
What are the ureters made of?
Smooth visceral muscle
What is the effect of parasympathetic stimulation on the ureters? Sympathetic?
Parasympathetic - increased contractions
Sympathetic - decreased contractions
In what kind of situation does the ureterorenal reflex occur?
Painful ones, like a kidney stone
Do the ureters contain pain fibers?
Yes, many
What is the term for the process of the urinary bladder emptying when it is filled?
Micturition
What is unique about the series of contractions during micturition?
Self-regenerative: initial contraction of detrusor muscle causes further activation of stretch receptors to lead to more contraction and repetition
Urination can be facilitated or inhibited by what neurological brain centers?
Pons and cerebral cortex
What muscles are contracted during voluntary urination?
Abdominal muscles
What does the rate of back leakage of sodium in tubular reabsorption depend on?
Permeability of the tight junction
Rate of bulk flow reabsorption into the peritubular capillaries
As the concentration of sodium in the proximal tubule increases, how is the reabsorption rate of sodium affected?
Also increases
Sodium transport in the proximal tubules obey the principles of which transport concept?
Gradient time transport
What kind of flow rate of tubular fluid exerts a greater amount of sodium being reabsorbed?
Slower flow rate
What other absorption function is coupled with sodium reabsorption in the tubules?
Passive water absorption
How is water absorbed passively at the same time as sodium reabsorption?
Osmosis occurs between highly permeable cells of the proximal tubule
What effect does the osmosis of water in the proximal tubules on solutes?
Solvent drag occurs and the movement of water carries the solutes with it
What kind of transport moves chloride from the negatively charged tubular lumen?
Passive
What kind of transport moves chloride and sodium across the tubular membrane?
Secondary active transport (co-transport)
What happens to urea concentration as water is reabsorbed?
Increases (causes passive reabsorption of urea)
Where are urea transporters found?
Medullary collecting duct
Is the proximal tubule very permeable to urea?
Not really
Why is it important that the tubule NOT be very permeable to urea?
Allows for large amounts of urea to be excreted
Where is 65% of the filtered water and sodium reabsorbed?
Proximal tubule before reaching loop of Henle
What is the primary tool to reabsorb sodium, chloride, and water?
Sodium-potassium ATPase pump
What substances are rapidly reabsorbed in the first half of the proximal tubule?
Sodium, glucose, amino acids, and water
A high concentration of which ions are left in the second half of the proximal tubule?
Chloride
What is the proximal tubule highly permeable to?
Water (providing constant osmolarity)
